Slide 1

Impact of fire on the inputs of heat, moisture and carbon dioxide to the atmosphere in Australian tropical savannas and feedbacks to regional climate Jason Beringer, Lindsay Hutley and Nigel Tapper Australia New Zealand Climate Forum Tropical Savannas CRC Slide 2 Overview Introduction Fire in the North Effect of fire on the energy balance Effect of fire on local to regional climate The savanna fire experiment Preliminary results Conclusions Slide 3 Australias Tropical Savanna Lands Lie entirely within the tropics Cover 20% of the land mass with 5% of the population Produce 25% of the countrys export income Are characterized by, and to a large extent are dependent on, heavy seasonal burning Slide 4 Slide 5 Fire Scars Mapped in 1999 1997, 1998 and 1999 ~ 250,000 km 2 burned in each dry season Slide 6 In 1992 7.4 x 10 6 ha burnt equaling 5.5% of the NT land area Beringer, Packham and Tapper, 1995 Slide 7 Emissions from N.T. biomass burning in 1992 29.5 x 10 6 tonnes of biomass consumed; emissions were:- 11.3 Tg carbon as carbon dioxide 1.02 Tg carbon as carbon monoxide 0.005 Tg carbon as particulate matter 0.026 Tg nitrogen as nitrous oxides [NB. 1 Tg (teragram) = 10 12 grams] Beringer, Packham and Tapper, 1995 Slide 8 Regional Transport TOMS Aerosol Loading in Australian Region, 6 October 2000 SE Transport NW Transport Wain, Tapper and Mills, 2001 Slide 9 Percent Change in Cumulative FDI for 2xCO 2 Williams, Karoly and Tapper, 2001 Slide 10 Carbon Cycle of Northern Territory Savanna Savanna sink strength 60 Mt C y - 1 Fire emissions 9 20 Mt C y -1 (15-35% of sequestered C each year) CRC for Tropical Savannas, 2001 Slide 11 Changes in energy balance following fire. Q* = Net radiation Q* Q G = Ground heat flux = Q G Q E = Latent heat flux + Q E Q H = Sensible heat flux + Q H Increase Decrease Fire and the surface energy balance Slide 12 Impact of Savanna Fire Scars on Surface Energy Balance Scholes and Walker (1993) halving of albedo of African savanna from ~0.13 to around 0.06, with recovery over 6 8 weeks Hutley (unpub) eddy correlation measurements of evapotranspiration over north Australian savanna after a mid- dry season fire showed complete cessation of evapotranspiration, with a recovery over the subsequent 8 weeks Slide 13 Results of Hutley (unpub) Slide 14 Albedo 0.19 Unburned 0.05 Burned Impact of Fire Scars on Surface Energy Balance in Non-Savanna Environments Slide 15 Burned and Unburned Tundra Radiation and Energy Fluxes, August 2, 2000 Q H ~100-150 Wm -2 Burned Q*~100-150 Wm -2 > Burned Slide 16 Atmospheric Implications of Local- to Regional Scale Variations in the Surface Energy Balance Knowles (1993) in a theoretical and modelling study of forest fire scars in Alaska showed that, depending on the aerodynamic changes to vegetation following fire, enhanced sensible fluxes over patches of burnt landscape (on the order of 10 km in diameter) would be likely to produce localized areas of convergence and divergence and associated mesoscale circulation systems Fire Scars Slide 17 Atmospheric Implications of Local- to Regional Scale Variations in the Surface Energy Balance Fire Scars Knowles, 1993 480 km 2 fire scar in Alaska Slide 18 Atmospheric Implications of Local- to Regional Scale Variations in the Surface Energy Balance Fei Chen et al.(2001) has shown quite convincingly how surface modification by a wildfire burn influences the path of the major convective event that caused the 1996 Buffalo Creek flash flood in Colorado. Fire Scars Slide 19 The Savanna Fire Experiment (SaFE) Slide 20 Hypothesis 1 Fire causes a threshold change in savanna energy exchange with the atmosphere Immediately following dry season fires, there is a measurable decrease in savanna albedo, a decrease in evapotranspiration and increase in soil heat and sensible heat fluxes, followed by an extended recovery phase. Slide 21 Hypothesis 2 Alterations in savanna energy exchange following fire have important impacts on atmospheric circulation and water balance Changes in atmospheric heating rates and associated horizontal pressure gradients will produce atmospheric motion at a range of scales. This may modify patterns of precipitation and potentially affect the strength of the Australian monsoon. Soil moisture may be affected at equivalent scales. Slide 22 Influence of landscape scale fires on the Australian Monsoon The development of heat-lows and linking of the troughs in spring-summer from radiant heating is needed for Monsoon development This provides the continental axis for the ITCZ moving onto Australia Fire on large scales could have an influence Queensland trough West coast trough Zonal trough Pilbara LowCloncurry Low Slide 23 Hypothesis 3 Future climate change will alter the north Australian fire regime, with consequent feedbacks to vegetation and climate The climate associated with a projected doubling of CO 2 will lead to a more extreme fire regime for northern Australia and a likely increase in area burnt each fire season. This will lead to dynamic changes in vegetation and climate in a series of complicated feedbacks. Slide 24 Preliminary Results A pilot study was undertaken this dry season Eddy covariance measurements of heat, moisture and carbon dioxide fluxes Measurements over burned and unburned sites Slide 25 Effects of Fire: Carbon dioxide released through biomass burningCarbon dioxide released through biomass burning Decreased albedoDecreased albedo Scorching of the leavesScorching of the leaves Trees shut down and do not photosynthesiseTrees shut down and do not photosynthesise Slide 26 Fire Slide 27 Evapotranspiration is severely reducedEvapotranspiration is severely reduced Slide 28 Therefore more solar energy goes into heating the atmosphereTherefore more solar energy goes into heating the atmosphere Slide 29 Savanna changes from sink to sourceSavanna changes from sink to source Slide 30 Conclusions Fire is an integral part of Tropical Australia Emissions from fire contributes to the enhanced greenhouse Fire alters the heat and moisture balance This may in turn influence local to regional climate Changes in the carbon balance are also important